This invention relates to magnetic heads used in magnetic recording devices, such as magnetic disk or floppy disk devices, for magnetically writing and reading data from recording medium.
Reference is made to FIGS. 12-17 wherein a conventional magnetic head is shown.
FIGS. 12 and 13 are a side elevational view and a top plan view of a conventional magnetic head such as shown in U.S. Pat. No. 4,646,184. This magnetic head includes a write/read head 1, an erase head 2, a gap 3, an erase gap 4, a central spacer 5, a magnetic core 6 with legs 6a, 6b forming the gap 3, a magnetic core 7 with legs 7a, 7b forming the gap 4, a write/read coil 8, an erase coil 9, and another magnetic material 10 having a magnetic flux density lower than that of the magnetic core 6. Gr is the read gap, Gw the write gap, and T the write/read track width.
FIGS. 14-16 illustrate the conventional magnetic head and the data track, the write operation, and the read operation, respectively, wherein 11, 11a, 11b, 11c, and 11d are the data track, 12a and 12b are the guard band between the data tracks, A is the direction in which the recording medium is advancing.
FIG. 17 is a block diagram of a write signal unit for controlling the magnetic head. The write signal unit includes a modulation circuit 13, a write amplifier 14, a control circuit 15, and an erase circuit 16.
In operation, a high-frequency write data signal is modulated in the modulation circuit 13 and amplified in the write amplifier 14, and transmitted to the write/read head 1 via the write read coil 8. The electrical signal in the write read coil 8 excites the magnetic core 6 of the write/read head 1 by electromagnetic induction. Part of the magnetic flux thus produced becomes leakage flux through the gap 3 to magnetize the recording medium for writing data thereon.
For reading the data, when the write/read head 1 moves over the recording medium, the leakage flux enters the magnetic core 6 via the gap 3 and interlinks with the coil 8 to induce a voltage therein.
Thus, the material and width of the gap 3 have great influences on the write/read characteristics. For writing, the gap and the saturated flux density of the core 6 should be large and high respectively. For reading, the gap should be small in order to pick up accurately changes of the leakage flux from the recording medium. In this case, the saturated flux density of the magnetic core 6 may be low. The write head and the read head are used to be separated but, today, they are integrated as a write/read head. Thus, today's gap of the write/read head is not an ideal but a compromise of those for write and read heads.
The aforementioned write/read head 1 has been developed to improve this drawback. The magnetic material 10 having a saturated flux density lower than that of the magnetic core 6 is secured to the end face 6x of a core leg 6a so that the write gap Gw made by the ends faces 6x, 6y of the legs 6a, 6b is used for writing while the read gap Gr made by the magnetic material 10 and the end face 6y of the leg 6b is used for reading. That is, during writing, the amount of leakage flux from the wide gap Gw made of the magnetic core of a high saturated flux density becomes large so that the recording medium is highly magnetized. On the other hand, during reading, the narrow gap Gr made of a magnetic material of low saturated flux density makes it possible to follow small changes in the leakage flux from the recording medium.
As shown in FIGS. 12 and 13, the erase head 2 is integrated with the write/read head 1 via the central spacer 5 to form a magnetic head. The erase head 2 has two erase gaps 4 about either end of the write/read track width T of the write/read head 1. When the write/read head 1 writes a data signal, the erase circuit 16 receives a signal from the control circuit 15 to supply electric current to the erase coil 9, thereby operating the erase head 2.
FIG. 14 illustrates that the erase head 2 is erasing both edge portions of the data track 11 on which the data signal has been written by the write/read head 1. In general, when writing and/or reading data signals from the recording medium is repeated or carried out in another device, the magnetic head gets out of position. Consequently, not all part of a data signal is erased as a new data signal is written. This remaining signal or a signal from the adjacent track makes noise during reading. For this reason, the both edges of a data track on which a data signal has been written are erased to eliminate this noise.
As shown in FIG. 15, there are guard bands 12a, 12b between the data tracks 11a, 11b, 11c which are made by the erase head 2. Thus, when the write/read head 1 gets out of position on the track 11b to write the next data signal, the new data track 11d is protected by guard bands 12a, 12b, thereby preventing noise generation.
Aa shown in FIG. 16, even if the write/read head 1 is out of position on the track 11d for reading, it does not pick up noise or a signal from the adjacent track 11a because of the presence of the guard band 12a.
As has been described above, the conventional magnetic head, which consists of the write/read head 1 and the erase head 2, is complex and expensive to make. In addition, it requires the control circuit, erase circuit, and erase coil for operating the erase head, making the whole device complex and expensive.